This is a U.S. national stage of application No. PCT/DE99/03880, filed on Nov. 29, 1999. Priority is claimed on that application and on the following application: Country: Germany, Application No.: 198 57 779.6, Filed: Dec. 04, 1998.
The invention pertains to a crane, especially a self-propelled crane with a base structure and a revolving superstructure mounted thereon.
Cranes on which a mast and a superlift counterweight are installed are designed for high load moments. The counterweight moment required for this is produced by the superlift counterweight, which is set up a certain distance away from the crane. Various proposals have been offered for increasing the flexibility of the crane, that is, for increasing a crane""s ability to manage different load moments at different work sites with the least possible effort while preserving the mobility and rotatability of the crane.
One proposal for a mobile crane is described in DE 2,814,540 C2. A mobile crane with a revolving superstructure is disclosed. The superstructure is provided with a boom and a mast, which carries a superlift counterweight. Regardless of the load on the crane, this counterweight is supported on the ground in such a way that the superstructure can revolve. An air cushion is used to support the counterweight on the ground; the filling of this cushion can be varied in correspondence with the force measured on the mast. This arrangement also requires a compressor and the associated air lines, which does not make operations any easier. In addition, the distance between the superlift counterweight and the crane cannot be changed.
Another design is described in German Patent No. 195-0373
In this mobile crane, the superlift counterweight is designed in the form of a steerable cart, which is rigidly connected by link joints to the superstructure of the mobile crane. When a load is lifted, the counterweight cart is lifted also and can be swiveled together with the crane. It is a complicated matter to install and use a counterweight cart, and it can be difficult to set up, depending on the terrain. The distance between the counterweight cart and the mobile crane cannot be changed. In addition, the height to which the counterweight cart can be lifted cannot be adjusted as a function of the size of the load to be lifted. If the load were to decrease suddenly, the counterweight cart would not only crash to the ground but could even tip over, depending on how high it had been raised.
A variant of this known design is described in U.S. Pat. No. 4,258,852. The distance between the superlift counterweight and the mobile crane can be changed by a certain amount. For this purpose, the mast connected by variable guying to the superlift counterweight is tilted appropriately, and by replacement of certain lattice mast elements of the lattice mast holding the superlift counterweight a certain distance away from the crane, the distance can be changed by the length of the replaced lattice mast element. The disadvantage of this design is that the distance can be changed only by certain amounts and that rerigging is required to do it. In addition, the counterweight cart or carts must be raised by suspending a load. When two counterweight carts are provided, furthermore, the distance between them must also be adjusted appropriately.
In a prospectus from Manitowoc Engineering Co. (Complete Line Brochure), published in 1992, a mobile crane is presented under the trade name X-Spander, which has a continuously adjustable superlift counterweight. For this purpose, a frame element, which can be supported on the ground by raisable feet mounted at the end, is hinged to the rear of the superstructure. The superlift counterweight can be shifted continuously on this frame element to produce the desired countermoment. A bracket is mounted on the superstructure, the top of which is connected to the head of the boom by adjustable-length guying. The tip of the bracket is also connected by fixed guying to the end of the frame element. The disadvantage of this design is that the overhang is very large because of the fixed frame part, and the room required to accommodate it is not always present at the work site. In addition, the length of the frame element can be changed only by the attachment or removal of segments, which means that rigging is necessary each time. Neither in this proposed design nor in the case of the known crane described previously can the intrinsic weight of the base structure be used to increase the stability of the crane.
The task of the invention is to provide a crane of the general type in question, especially a mobile crane, by means of which, while preserving the ability to revolve, it is possible to adapt the crane easily to the desired load moments under the given work site conditions without rerigging.
According to the principle of the invention, the distance between the counterweight and the superstructure of the crane can be adjusted continuously in a fixed range by a frame element, which can move in the vertical plane, is mounted on the superstructure, and is connected to the superstructure in a gravity-actuated (nonpositive) manner, this frame element being provided with a means for directing the resultant of the counterweight force acting in the direction of gravity and the guying force produced by the suspended load into the superstructure.
The advantage of this arrangement is that, as a result of the gravity-actuated (nonpositive) connection of the frame element with the superstructure and as a result of the means mounted thereon, the intrinsic weight of the base structure can be used to increase stability. Depending on the direction of the resultant of the counterweight force and the guying force, the means acts either to support it or to counteract it. For example, a situation can be imagined in which, with the counterweight fully extended, the suspended load is not sufficient to raise the counterweight. The raising of the counterweight, however, is the condition which allows the crane to revolve. In this case, the resultant of the guying force and the counterweight force is negative, because the counterweight force acting in the direction of gravity is greater than the guying force produced by the load. In this simplified analysis, the frictional relationships at the deflection points and guyings have been left out of consideration. The means mounted on the frame part is now activated in such a way that, by lifting the frame part vertically, an additional force is produced in the direction of the guying force and opposite the direction of the counterweight force, so that the counterweight is lifted and thus the crane can be revolved in spite of the small suspended load. In the opposite case, the means according to the invention ensures the stability of the crane when the maximum load is suspended, in that an additional force acting in the direction of the counterweight force and opposite the direction of the guying force is produced without the need to set down the counterweight.
The frame element can be installed with freedom of movement in the vertical plane, parallel to the plane of the superstructure; alternatively, it can be designed with freedom to swivel at one end. The swivel axis preferably intersects the rotational axis of the superstructure. The frame element has an axially stationary frame part connected to the superstructure and at least one frame part which can move in the axial direction, parallel to the stationary frame part. The axially movable frame part is preferably designed to telescope with the stationary frame part. The movable frame part can be moved by means of a rack, for example, or by means of a spindle. A piston-cylinder unit, which acts in the axial direction and which is hinged to the stationary frame part, has been found to be especially advantageous.
The means for directing the resultant force has at least one vertically-acting piston-cylinder unit. For space reasons and also to improve the distribution of the forces, one piston-cylinder unit is installed on the right and another on the left of the stationary frame part, one end of each of these units being hinged to the stationary frame part, the other end to the superstructure.
So that the design proposed here can be used not only as a superlift crane but also as a normal crane, the stationary frame part extends beyond the hinge point of the vertically-acting piston-cylinder unit, and this area can be bolted to a load-bearing structure which holds the counterweight. For this purpose, this area of the stationary frame part has a collar-like stiffening member and a rollway for the load-bearing structure holding the counterweight.
To increase the load capacity, additional counterweights can be provided on and locked to the load-bearing structure connected to the movable frame part. For safety reasons, support feet must be provided on the load-bearing structure , the feet extending down to a point close to the ground. To facilitate transport and handling, these support feet can be folded back onto the load-bearing structure. The additional counterweight can preferably be divided into individual stacks, each with its own frame. Each frame can be connected to at least four wheels, so that each individual stack can travel. This arrangement offers the advantage that the additional counterweight can be easily transported to the work site. In addition, the support feet on the load-bearing structure for the counterweight can be omitted, because the wheels fulfill this function. In the superlift operating mode, furthermore, the counterweight, including the additional counterweight, can be moved inward, even if the suspended load is not sufficient to lift them. If, after the counterweights have been moved inward, the counterweight moment is reduced sufficiently, the counterweight can be lifted by the suspended load, and the additional counterweights can be detached from the load-bearing structure.
Operation as a normal crane is still possible with the proposed overall design, in which case the counterweight is pushed inward and takes over the function of the known superstructure counterweight. The projecting length of the stationary frame part is selected so that, after the counterweight has been pushed past the end of the stationary frame part, stability toward the rear is still guaranteed. This offers the advantage that, without rerigging, additional counterweights can be mounted on and bolted to the load-bearing structure holding the counterweight. This can be accomplished by swiveling the crane or, in the case of a mobile crane, by driving it over them. This total counterweight, that is the counterweight plus the additional counterweights, is lifted by suspending an appropriate load, which thus allows the crane to revolve. The load moment can be increased even more by moving the movable frame part farther out. Because the movable frame part can be shifted continuously, the radius can be adjusted to suit the load as work site conditions permit. The minimum radius is determined by the layout of the crane. Various intermediate radii can be obtained by shifting the counterweight toward the rear until the point of static moment at the rear is reached. The maximum radius is determined, first, by the maximum distance by which the movable frame part can be moved and, second, by the overall structure available to absorb the total ballast. In accordance with a first embodiment, the tip of the mast is connected to the counterweight by guying of adjustable length passing over a braced support. With this arrangement, the mast, the length-adjustable guying between the mast and the counterweight, and the guying between the mast and the boom move in correspondence with the displacement of the counterweight. This requires an appropriate control system to coordinate the axial displacement of the counterweight with the swiveling motion of the mast. To reduce the effort required for this, it is proposed as an alternative that the tip of the mast be connected to the counterweight by fixed guying and to the stationary frame part of the frame element by adjustable-length guying passing over a hinged, braced support. In this arrangement, the tip of the braced support is connected by fixed guying to the load-bearing structure of the counterweight. This offers the advantage that, in superlift operating mode, only the fixed guying between the mast and the counterweight is active. The length of the fixed guying between the tip of the mast and the loadbearing bearing structure of the counterweight, which length changes upon displacement of the counterweight, is negligible in comparison to the height of the erected mast and under consideration of the fact that the counterweight shifts by only a few meters in superlift operating mode. When operation is changed back to normal, the fixed guying is removed and only the adjustable-length guying is active. So that both variants can be realized, the lower end of the forked, braced support, which holds a winch for changing the adjustable-length guying in conjunction with a block and pulley, can be hinged as desired-either to the load-bearing structure holding the counterweight or to the stationary frame part of the frame element.
The advantages cited above can be summarized by saying that they produce a significant improvement in operating convenience, in the sense that, under consideration of the space limitations prevailing at the work site, any of the intermediate stages between normal operating mode and superlift operating mode, which provides the greatest countermoment, can be obtained without rerigging.